1. Field of the Invention
The present invention relates to a drive unit for a switching element having an excess current protection function that is capable of being applied to, for example, a rotating electrical machine.
2. Description of the Related Art
As shown, for example, in JP-B-3474775, as this type of device, a device is known that includes an excess current protection circuit that protects a switching element (such as an insulated-gate bipolar transistor [IGBT]) from excess current. Specifically, the device includes a resistor and a comparator. The resistor is connected between a sense terminal and an output terminal of the switching element. The comparator compares a sense voltage and a threshold voltage. The sense voltage is the difference of electric potential between both ends of the resistor. Here, the sense terminal is a terminal that outputs a minute current having correlation with a current flowing between the input and output terminals of the switching element.
In a configuration such as that described above, when a collector current becomes excessively large and the sense voltage is judged to exceed the threshold voltage, a judgment is made that excess current is flowing to the switching element. The switching element is then switched to an OFF state. As a result, the switching element is protected from the excess current. Decrease in the reliability of the switching element can be prevented.
However, the inventors of the present invention have come across the following issue. Even when excess current is flowing to the switching element, the flow of excess current to the switching element cannot be promptly detected because the actual sense voltage is lower than an initial assumed value based on the collector current. When the excess current cannot be promptly detected, the reliability of the switching element may decrease.
Therefore, regarding drive units for a switching element having an excess current protection function, a new drive unit for a switching element is desired that is capable of promptly detecting the flow of excess current.